1. Field of the Invention
The present invention relates to an organic electroluminescent display (ELD) device, and more particularly, to an array substrate for an organic electroluminescent display device and a method of fabricating the same.
2. Discussion of the Related Art
An organic electroluminescent display (ELD) device, which is a type of flat panel display, is a self-emission type display. In general, the organic ELD device emits light by injecting electrons from a cathode and holes from an anode into an emission layer, combining the electrons with the holes, generating an exciton, and transitioning the exciton from an excited state to a ground state. Accordingly, the organic ELD device does not require an additional light source and has a light weight, thin profile, and compact size.
There are two types of organic ELD devices: passive matrix type and active matrix type. While both the passive matrix organic ELD device and the active matrix organic ELD device have simple structures and are formed by a simple fabricating process, the passive matrix organic ELD device requires a relatively high amount of power to operate. In addition, the display size of a passive matrix organic ELD device is limited by its structure. Furthermore, as the number of conductive lines increases, the aperture ratio of a passive matrix organic ELD device decreases. In contrast, active matrix organic ELD devices are highly efficient and can produce a high-quality image for a large display with a relatively low power.
FIG. 1 is a cross-sectional view of a bottom emission type organic electroluminescent display device according to the related art. In FIG. 1, an organic ELD device 1 includes first and second substrates 10 and 5 attached to each other by a sealant 15 with a space therebetween. An array element layer 14 including a thin film transistor (TFT) T is formed on the first substrate 10. In addition, a first electrode 70, an organic electroluminescent (EL) layer 85 and a second electrode 90 are sequentially formed on the array element layer 14. The first electrode 70 is formed in each pixel region P, and the organic EL layer 85 separately displays red, green, and blue colors in each pixel region P. The organic EL layer 85 for different colors may be formed of different materials corresponding to the colors.
The organic ELD device 1 is encapsulated by attaching the first substrate 10 and the second substrate 5 with the sealant 15. The second substrate 5 includes a moisture absorbent material 9 to eliminate moisture and oxygen that may penetrate into the organic EL layer 85. After etching a portion of the second substrate 5, the etched portion is filled with the absorbent material 9 and the filled absorbent material 9 is fixed with a tape 7. Since the first electrode 70 is formed of a transparent conductive material, light from the organic EL layer 85 is emitted at a bottom of the organic ELD device 1 through the first electrode 70.
FIG. 2 is a plane view an array substrate for an organic electroluminescent display device according to the related art. In FIG. 2, a gate line 20, a data line 30 and a power line 31 are formed on a substrate 10. The gate line 20 crosses the data line 30 to define a pixel region P, and the power line 31 is parallel to and spaced apart from the data line 30. A switching element Ts is connected to the gate line 20 and the data line 30, and a driving element Td is connected to the switching element Ts. The switching element Ts includes a first gate electrode 25, a first active layer 40a, a first ohmic contact layer (not shown), a first source electrode 32a and a first drain electrode 34a. In addition, the driving element Td includes a second gate electrode 26, a second active layer 40b, a second ohmic contact layer (not shown), a second source electrode 32b and a second drain electrode 34b. Portions of the data line 30 and the power line 31 may be used as the first and second source electrodes 32a and 32b, respectively. A transparent first electrode 70 in the pixel region P is connected to the second drain electrode 34b through a first contact hole CH1. Further, a transparent connection line 75 is connected to the first drain electrode 34a through a second contact hole CH2 and the second gate electrode 26 through a third contact hole CH3, thereby connecting the first drain electrode 34a and the second gate electrode 26.
FIG. 3 is a cross-sectional view taken along a line III-III of FIG. 2. In FIG. 3, a gate insulating layer 45 is formed on the second gate electrode 26. The second active layer 40b and the second ohmic contact layer 41b are sequentially formed on the gate insulating layer 45, and the second source and drain electrodes 32b and 34b are formed on the second ohmic contact layer 41b. The second source and drain electrodes 32b and 34b are spaced apart from each other, and the second active layer 40b is exposed through a space between the second source and drain electrodes 32b and 34b. 
A first passivation layer 65 having the first contact hole CH1 is formed on the second source and drain electrodes 32b and 34b, and a color filter layer 78 is formed on the first passivation layer 65. Although not shown in FIG. 3, the color filter layer 78 includes red, green and blue color filters each corresponding to the pixel region P (of FIG. 2). The transparent first electrode 70 connected to second drain electrode 34b is formed on the color filter layer 78, and a second passivation layer 66 is formed on the first electrode 70. The second passivation layer 66 has a fourth contact hole CH4 exposing the first electrode 70 corresponding to the first contact hole CH1. The organic EL layer 85 is formed on the first electrode 70, and the second electrode 90 is formed on the organic EL layer 85.
The second source and drain electrodes 32b and 34b and the data line 30 are formed of a metallic material, for example, molybdenum (Mo). While the first passivation layer 65 is patterned to form the first contact hole CH1, the second drain electrode 34b corresponding to the first contact hole CH1 is also removed. Accordingly, the first electrode 70 contacts side surfaces of the second drain electrode 34b and the substrate 10 corresponding to the first contact hole CH1. As a result, the light from the organic EL layer 85 corresponding to the first contact hole CH1 is emitted through the first electrode 70. Since the light corresponding to the first contact hole CH1 does not pass through the color filter layer 78, the light corresponding to the first contact hole CH1 causes a light leakage. In addition, the second drain electrode 34b may be over-etched to form an overhang structure where the second drain electrode 34b is not exposed through the first contact hole CH1, or the gate insulating layer may be etched to generate step differences on side surfaces of the first contact hole CH1. Accordingly, when the first electrode 70 is formed on the first passivation layer 65, the first electrode 70 may not contact the second drain electrode 34b because of the overhang structure or may be broken to cause an electric opening between the switching element Ts and the driving element Td.